Intrathecal morphine does not prevent chronic postsurgical pain after elective Caesarean delivery: a randomised controlled trial

Abstract

BackgroundMorphine is frequently added to spinal anaesthesia for Caesarean delivery. We aimed to determine whether intrathecal morphine for spinal anaesthesia decreases the risk of chronic postsurgical pain (CPSP). MethodsIn this randomised, double-blind, placebo-controlled trial, 290 healthy parturients undergoing elective Caesarean delivery were randomly assigned in a 1:1 ratio to receive either intrathecal morphine 100 μg (n=145) or normal saline (control; n=145) as a part of spinal anaesthesia. Anaesthetic care and postoperative pain management were standardised in all patients. The primary outcome was the incidence of CPSP at 3 months. Secondary outcomes included CPSP at 6 months, pain severity, and pain interference, measured by the Brief Pain Inventory questionnaire using an 11-point numeric rating scale, at 3 and 6 months after the surgery. ResultsTwo hundred and seventy-six patients completed the 3-month follow-up, 139 in the morphine group and 137 in the placebo group. The incidences of CPSP at 3 months were 19% (27 of 139) in the morphine group and 18% (25 of 137) in the placebo group (odds ratio, 1.08; 95% confidence interval, 0.59–1.97; P=0.803). At 6 months, CPSP was present in 23 of 139 (16%) morphine group patients compared with 19 of 137 (14%) in the placebo group (odds ratio, 1.23; 95% confidence interval, 0.63–2.38; P=0.536). Brief Pain Inventory questionnaire scores for pain severity and pain interference at 3 and 6 months were similar between groups. ConclusionsAdministration of morphine 100 μg as a component of spinal anaesthesia for elective Caesarean delivery failed to reduce the incidence of chronic pain at 3 and 6 months after surgery. Clinical trial registrationNCT03451695.